I'm trying to use the this launch file to operate my Relasens ecamera but it didn;t work because of some nodelet issue:

<!-- 
  Turtlebot is a bit low on horsepower...
  We use openni_camera here, turn everything on by default
  (allows the user to conveniently see everything when
  launching this on its own - use with 
  turtebot_rviz_launchers/view_robot.launch to visualise)
  and provide args to disable them so you can optimise the
  horsepower for your application.

  For an example of disabling processing modules, check
  any of the turtlebot_rapps (e.g. android_make_a_map.launch
  only enables scan_processing for depthimage_to_laserscan and
  rgb_processing for the android tele-view).
-->
<launch>
  <!-- "camera" should uniquely identify the device. All topics are pushed down
       into the "camera" namespace, and it is prepended to tf frame ids. -->
  <arg name="camera"      default="camera"/>
  <arg name="publish_tf"  default="false"/>
  <arg name="3d_sensor"   default="$(env TURTLEBOT_3D_SENSOR)"/>  <!-- kinect, asus_xtion_pro -->

  <!-- Factory-calibrated depth registration -->
  <arg name="depth_registration"              default="true"/>
  <arg     if="$(arg depth_registration)" name="depth" value="depth_registered" />
  <arg unless="$(arg depth_registration)" name="depth" value="depth" />

  <!-- Processing Modules -->
  <arg name="rgb_processing"                  default="true"/>
  <arg name="ir_processing"                   default="true"/>
  <arg name="depth_processing"                default="true"/>
  <arg name="depth_registered_processing"     default="true"/>
  <arg name="disparity_processing"            default="true"/>
  <arg name="disparity_registered_processing" default="true"/>
  <arg name="scan_processing"                 default="true"/>

  <!-- Worker threads for the nodelet manager -->
  <arg name="num_worker_threads" default="4" />

  <!-- Laserscan topic -->
  <arg name="scan_topic" default="scan"/>

  <include file="$(find turtlebot_bringup)/launch/includes/3dsensor/$(arg 3d_sensor).launch.xml">
    <arg name="camera"                          value="$(arg camera)"/>
    <arg name="publish_tf"                      value="$(arg publish_tf)"/>
    <arg name="depth_registration"              value="$(arg depth_registration)"/>
    <arg name="num_worker_threads"              value="$(arg num_worker_threads)" />

    <!-- Processing Modules -->
    <arg name="rgb_processing"                  value="$(arg rgb_processing)"/>
    <arg name="ir_processing"                   value="$(arg ir_processing)"/>
    <arg name="depth_processing"                value="$(arg depth_processing)"/>
    <arg name="depth_registered_processing"     value="$(arg depth_registered_processing)"/>
    <arg name="disparity_processing"            value="$(arg disparity_processing)"/>
    <arg name="disparity_registered_processing" value="$(arg disparity_registered_processing)"/>
  </include>

   <!--                        Laserscan 
     This uses lazy subscribing, so will not activate until scan is requested.
   -->
  <group if="$(arg scan_processing)">
    <node pkg="nodelet" type="nodelet" name="depthimage_to_laserscan" args="load depthimage_to_laserscan/DepthImageToLaserScanNodelet $(arg camera)/$(arg camera)_nodelet_manager">
      <!-- Pixel rows to use to generate the laserscan. For each column, the scan will
           return the minimum value for those pixels centered vertically in the image. -->
      <param name="scan_height" value="10"/>
      <param name="output_frame_id" value="$(arg camera)_depth_frame"/>
      <param name="range_min" value="0.45"/>
      <remap from="image" to="$(arg camera)/$(arg depth)/image_raw"/>
      <remap from="scan" to="$(arg scan_topic)"/>

      <!-- Somehow topics here get prefixed by "$(arg camera)" when not inside an app namespace,
           so in this case "$(arg scan_topic)" must provide an absolute topic name (issue #88).
           Probably is a bug in the nodelet manager: https://github.com/ros/nodelet_core/issues/7 -->
      <remap from="$(arg camera)/image" to="$(arg camera)/$(arg depth)/image_raw"/>
      <remap from="$(arg camera)/scan" to="$(arg scan_topic)"/>
    </node>
  </group>
</launch>

Without using the nodelete like below, it works, I just want to know possible reasons for this occurence:

<!-- 
  Turtlebot is a bit low on horsepower...
  We use openni_camera here, turn everything on by default
  (allows the user to conveniently see everything when
  launching this on its own - use with 
  turtebot_rviz_launchers/view_robot.launch to visualise)
  and provide args to disable them so you can optimise the
  horsepower for your application.

  For an example of disabling processing modules, check
  any of the turtlebot_rapps (e.g. android_make_a_map.launch
  only enables scan_processing for depthimage_to_laserscan and
  rgb_processing for the android tele-view).
-->
<launch>
  <!-- "camera" should uniquely identify the device. All topics are pushed down
       into the "camera" namespace, and it is prepended to tf frame ids. -->
  <arg name="camera"      default="camera"/>
  <arg name="publish_tf"  default="false"/>
  <arg name="3d_sensor"   default="$(env TURTLEBOT_3D_SENSOR)"/>  <!-- kinect, asus_xtion_pro -->

  <!-- Factory-calibrated depth registration -->
  <arg name="depth_registration"              default="true"/>
  <arg     if="$(arg depth_registration)" name="depth" value="depth_registered" />
  <arg unless="$(arg depth_registration)" name="depth" value="depth" />

  <!-- Processing Modules -->
  <arg name="rgb_processing"                  default="true"/>
  <arg name="ir_processing"                   default="true"/>
  <arg name="depth_processing"                default="true"/>
  <arg name="depth_registered_processing"     default="true"/>
  <arg name="disparity_processing"            default="true"/>
  <arg name="disparity_registered_processing" default="true"/>
  <arg name="scan_processing"                 default="true"/>

  <!-- Worker threads for the nodelet manager -->
  <arg name="num_worker_threads" default="4" />

  <!-- Laserscan topic -->
  <arg name="scan_topic" default="scan"/>

  <include file="$(find turtlebot_bringup)/launch/includes/3dsensor/$(arg 3d_sensor).launch.xml">
    <arg name="camera"                          value="$(arg camera)"/>
    <arg name="publish_tf"                      value="$(arg publish_tf)"/>
    <arg name="depth_registration"              value="$(arg depth_registration)"/>
    <arg name="num_worker_threads"              value="$(arg num_worker_threads)" />

    <!-- Processing Modules -->
    <arg name="rgb_processing"                  value="$(arg rgb_processing)"/>
    <arg name="ir_processing"                   value="$(arg ir_processing)"/>
    <arg name="depth_processing"                value="$(arg depth_processing)"/>
    <arg name="depth_registered_processing"     value="$(arg depth_registered_processing)"/>
    <arg name="disparity_processing"            value="$(arg disparity_processing)"/>
    <arg name="disparity_registered_processing" value="$(arg disparity_registered_processing)"/>
  </include>

   <!--                        Laserscan 
     This uses lazy subscribing, so will not activate until scan is requested.
   -->
  <group if="$(arg scan_processing)">
    <node pkg="nodelet" type="nodelet" name="depthimage_to_laserscan" args="load depthimage_to_laserscan/DepthImageToLaserScanNodelet $(arg camera)/$(arg camera)_nodelet_manager">
      <!-- Pixel rows to use to generate the laserscan. For each column, the scan will
           return the minimum value for those pixels centered vertically in the image. -->
      <param name="scan_height" value="10"/>
      <param name="output_frame_id" value="$(arg camera)_depth_frame"/>
      <param name="range_min" value="0.45"/>
      <remap from="image" to="$(arg camera)/$(arg depth)/image_raw"/>
      <remap from="scan" to="$(arg scan_topic)"/>

      <!-- Somehow topics here get prefixed by "$(arg camera)" when not inside an app namespace,
           so in this case "$(arg scan_topic)" must provide an absolute topic name (issue #88).
           Probably is a bug in the nodelet manager: https://github.com/ros/nodelet_core/issues/7 -->
      <remap from="$(arg camera)/image" to="$(arg camera)/$(arg depth)/image_raw"/>
      <remap from="$(arg camera)/scan" to="$(arg scan_topic)"/>
    </node>
  </group>
</launch>